This invention relates to power-driven conveyors generally and, more particularly, to spiral conveyors and conveyor belts therefor.
Spiral conveyors are well known in the bakery and frozen food industries. By providing a multi-layer helical conveying path, a spiral conveyor requires significantly less floor space than a conventional horizontal conveyor. Such a compact conveyor is especially useful for conveying products inside ovens and freezers.
A typical spiral conveyor includes a cylindrical tower, cage, or drum rotating about a vertical axis. A conveyor belt is wrapped helically around the rotating drum. As the drum rotates, it drives the belt by its engagement with the inside edge of the belt. Various take-up and feed sprockets define the belt""s conveying path from the point of its exit from the drum to its entry point back onto the drum.
The drum is driven in an overdrive condition in which its outer driving surface moves at a speed greater than the speed of the belt. Although slip between the belt and the drum is desirable, too much slip means inefficient driving engagement. To improve the driving engagement, the inside edge of the belt or the outer surface of the drum often includes protrusions or frictional elements that increase the friction or the engagement between drum and belt. But, in increasing the horizontal friction, the vertical friction is also increased. This makes it more difficult for the belt to ascend or descend, as it must, in following its helical path around the drum.
Conveyor belts with rollers at the edges are used in low-friction applications. The rollers engage bearing surfaces on side rails in rolling contact to reduce the friction between belt and rail, especially as a belt negotiates a turn. But the rollers in such belts are arranged to rotate about a vertical axis so as to reduce horizontal friction. Such a belt would not work well in a spiral conveyor system.
A spiral conveyor embodying features of the invention comprises a cylindrical tower with an outer surface and a modular conveyor belt traveling around it in a helical path. The tower rotates about a vertical axis. The belt is arranged to move in a helical path around the tower. An inner belt edge is proximate to the outer surface of the tower. Rollers disposed at the inner edge engage the outer surface of the tower in rolling contact. The rollers have an axis of rotation oriented to provide less friction between the conveyor belt and the tower for the component of motion up or down the tower than for the component of motion circumferentially around the tower.
One version of the conveyor belt comprises a series of rows of belt modules. Each row extends in a longitudinal direction from a first end to a second end, in a lateral direction from a first side edge to a second side edge, and in a thickness direction from a top side to a bottom side. Consecutive rows are hingedly connected end to end to form the conveyor belt. A first roller extends outward from the first side edge of selected rows of belt modules. The roller has an axis of rotation oriented generally perpendicular to the lateral direction. The axis of rotation forms a non-zero angle with the thickness direction.